Time interval generating circuits



Dec. 13, 1960 F. G. STEELE TIME INTERVAL GENERATING CIRCUITS 3 Sheets-Sheet 1 Filed Nov. 17, 1955 W& I TI LZOVD 6. 57551.5

INVENTOR.

Dec. 13, 1960 F. G. STEELE TIME INTERVAL GENERATING cmcuns Filed Nov. 17, 1955 3 Sheets-Sheet 2 ram .0 6. 575646 INVENTOR.

arrow/4 MTMA JQNVQ $1 Dec. 13, 1960 STEELE 2,964,708

TIME INTERVAL GENERATING CIRCUITS Filed Nov. 17, 1955 5 Sheets-Sheet 3 I r Y 40406. 575545 0 INVENTOR.

arraelve'y United States Patent TIME INTERVAL GENERATING CIRCUITS Floyd G. Steele, La Jolla, Calif., assignor to Digital Control Systems, Inc., La Jolla, Calif.

Filed Nov. 17, 1955, Ser. No. 547,448

15 Claims. (Cl. 328-130) ties.

The present application is related in content to a prior filed copending US. application Serial No. 510,736 entitled Ordered Time Interval Computing Systems by the present inventor, filed May 24, 1955 which discloses methods and apparatus for converting analog input signals into corresponding electrically marked time intervals and for then converting these electrically marked time intervals into so called difunction signal trains which serve as suitable digital signals for use in electronic digital signals for use in electronic digital computation.

A typical time interval generating circuit, as shown in the identified copending application, responds to an applied electrical input signal by delivering at some time interval x afterwards an electrical output signal. Thus the input signal which orders the circuit marks the beginning or initiation of the time interval x while the output signal produced by the circuit marks the end of the time interval x. The duration of the time interval x is determined by some condition Within the circuit which is controlled by applied analog signals.

For example in one type of time interval generating circuit, shown in the identified application, the duration of the time interval x produced is proportional to the RC time constant of a series connected resistor R and capacitor C. If either R or C is varied, the x time interval is proportionally varied. By controlling either R or C (or both) with an analog signal, the time interval generating circuit may be made to serve as an analog-totime interval converter. For example, as described in the identified application, if an input analog signal is provided as a shaft displacement and the resistor R of the time interval generating circuit is provided as a potentiometer coupled to the shaft, then it is obvious that the resultant x time interval will be proportional to the shaft displacement In this manner the analog shaft displacement is converted by the circuit to an equivalent electrically marked time interval Moreover, in a circuit of the described type, an enormous amount of analog computation can be readily carried on within the circuit preliminary to the generation of an at time interval which represents the result of that analog computation. For example multiplication of two shaft displacements may be accomplished by coupling the po tentiometer R to one of the shafts and the capacitor C to the other shaft. Since the time interval x produced by the circuit is proportional to the product RC, it is clear that the resultant time interval generated by the circuit will therefore be proportional to the product of the two shaft displacements. Similarly addition of any number of shaft displacements can be accomplishedby providing resist-' ance R as the total resistance of a corresponding number of series connected variable resistors, each controlled by a corresponding shaft, so that the elfective total resistance is proportional to the sum of the shaft displacements. It is clear that mathematical functions of almost any order of complexity may be mechanized through utilization of relatively simple resistor-capacitor networks.

As shown in the identified copending application, each such resistor-capacitor network (called a charging circuit) had associated therewith a pulse generating circuit employing a single regenerative amplifier. In a complex system large number of amplifiers might therefore be required, the number of amplifiers corresponding to the number of charging circuit networks employed. However, it is the general experience of electrical engineers that the cost of an electrical system is directly proportional to the number of active elements employed while the reliability of a system is inversely related to the number of active elements. It is, therefore, highly desirable to reduce the number of amplifiers (active elements) required.

The present application discloses a modified form of time interval generating circuit in which a plurality of charging circuits share a common amplifier which serves selectively, on a time sharing basis, as an output device for all of the charging circuits. Thus in the modified time interval generating circuit of the present invention only a single active element is required to speak for a large number of charging circuits.

In one embodiment of the invention described in some detail in the present application, in which a common regenerative amplifier is shared by a plurality of charging circuits, each charging circuit has an input lead to which an input signal or actuating signal may be applied. If an input signal is applied to any selected one of the charging circuits, an output signal is produced thereafter by the regenerative amplifier at a time interval which is determined by the condition (the RC time constant, for example) of the selected charging circuit. In this manner any one of the charging circuits may be selectively interrogated to produce a corresponding time interval whose end is marked by a pulse produced by the common regenerative amplifier.

The charging circuits may be interrogated in fixed order as part of a regular sampling procedure. On the other hand, as described in the identified copending application Serial No. 510,736, the order of production of time intervals may be varied in accordance with decisions made pursuant to mathematical operations.

An additional feature offered by the circuit of the present invention is that the order of interrogation of the charging circuits may be controlled in a very direct manner by the time constants of the charging circuits, for if input signals are applied simultaneously to all of the charging circuits the resultant time interval produced will correspond to that charging circuit which has the shortest time constant. In this mode of operation therefore, the charging circuits themselves decide in a most direct and effective manner which circuit is to be interrogated at each simultaneous application of the input signals.

This decision making feature of the simultaneously operated charging circuits has great importance and usefulness in the field of automatic control. Suppose for example that a plurality of charging circuits were to be associated with a corresponding plurality of automatic production machines, each charging circuit monitoring the. supply of raw material for its associated machine. If input signals are simultaneously applied to all of the charging circuits, the resultant time interval produced would correspond to the charging circuit having the smallest time constant and would therefore represent the most deficient or lowest supply of raw material. Whenever this resultant time interval dropped below a predetermined minimum duration, a warning alarm could be issued whereupon the charging circuits could then be interrogated in serial order to discover which production machine had the deficient supply of raw material. There would be great time savings with such a scheme, since the relatively time consuming serial interrogation of the charging circuits would be performed relatively infrequently while the fast simultaneous interrogation of the charging circuits would be normal operation.

Another additional feature of the time interval generating circuits disclosed in the present application is that apparatus may be included for rendering their operation relatively independent of the absolute value of the voltages supplied to the circuits. As shown in the present application, if special precautions are not taken, the duration of an x times interval produced by a time interval generating circuit would be critically dependent upon the absolute magnitudes of the voltages supplied to the circuit. However it will be demonstrated that, if these voltages are supplied in a fixed ratio to one another, operation of the circuit and the duration of the resultant x time interval becomes largely independent of the absolute values of the supply voltages. Therefore in preferred embodiments of the invention apparatus is provided, as described in the present application, for supplying these voltages in the desired fixed ratio.

It is, therefore, an object of the invention to provide a time interval generating circuit in which a plurality of selectively operable passive element charging circuits share a common output circuit employing an active element.

It is another object of the invention to provide a time interval generating circuit including a plurality of charging circuits and a common output circuit wherein application of an input signal to any selected one of the charging circuits causes production of a resultant time interval corresponding to the condition of the selected charging circuit.

It is still another object of the invention to provide a time interval generating circuit including a plurality of charging circuits wherein simultaneous application of input signals to all of the charging circuits causes production of a resultant time interval corresponding to the condition of that charging circuit having the shortest time constant.

It is yet another object of the present invention to provide a time interval generating circuit whose operation is relatively independent of the absolute values of operating voltages supplied thereto. The novel features which are believed to be characteristic of the invention both as to its organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

Fig. 1 is a circuit diagram of a preferred embodiment of a time interval generating circuit according to the present invention.

Fig. 2 is a Waveform chart displaying, on a common time scale, voltage waveforms illustrative of the operation of the time interval generating circuit of the present invention.

Fig. 3 is a circuit diagram illustrating a modified form of time interval generating circuit.

Fig. 4 is a circuit diagram illustrating another modification of the time interval generating circuit of the present invention.

Fig. 5 is a graph displaying a voltage waveform produced during operation of the time interval generating circuits of the present invention.

Referring now to the drawings there is shown in Fig. 1, a time interval generating circuit according to the in vention which includes a plurality of charging circuits 1, 2, etc. through n, these charging circuits being coupled to and sharing a common pulse generator 11, having an output conductor 12. Each of the charging circuits includes a series R-C (resistor-capacitor) network, whose time constant (the product of R and C) is controlled by externally applied analog signals.

Charging circuit 1, for example contains a series connected capacitor C and variable resistor R the value of R being controlled as shown in Fig. 1 for purposes of illustration by the rotational position of an external shaft, shaft 1, which is coupled to resistor R this rotational position of the shaft being designated as analog signal S The other charging circuits 2 through It embody similar R-C networks and are similarly controlled by analog signals S through S respectively as shown in Fig. 1. Moreover, each of the charging circuits 1 through It includes an associated input conductor, these input conductors being designated conductor 1 (abbreviated er. 1) conductor 2 through conductor n respectively.

In the overall functioning of time interval generating circuit 16*, upon application of an appropriate electrical input signal to the input conductor of a selected charging circuit, an output pulse 1., is produced by pulse generating circuit 11 and applied to output conductor 12 after a time interval x which is determined by the R-C time constant of the selected charging circuit. In this manner any one of charging circuits 1 through n may be selectively interrogated to produce a corresponding time interval x whose end is marked by the output pulse I produced by pulse generator 11.

Moreover, in the operation of time interval generating circuit 10, if input signals are simultaneously applied to all of the input conductors the resultant time interval x elapsing between application of the signals and production of an output pulse I will correspond to the condition of that charging circuit having the smallest time constant. In this mode of operation, therefore, the charging circuits themselves decide in a direct and effective manner which charging circuit is to be selected at each simultaneous application of the input signals.

Considering now the detailed structure of charging circuits 1 through it and referring to charging circuit 1 for purposes of example, it is seen that within charging circuit 1, variable resistor R is connected between terminal 15 and one terminal of a source (not shown) of high positive potential V, the other terminal of the source being grounded, while capacitor C is connected between terminal 15 and ground. Terminal 15 is connected through a conductor 17 to the anodes of a pair of diodes D and D and to the cathode of a diode D The cathodes of diodes D and D are connected to an output conductor 0 and conductor 1, respectively. The anode of diode D is connected to one terminal of a source (not shown) of potential V which may for example have a value of +15 volts, the other terminal of the source being grounded. The remaining charging circuits 2 through n have a substantially identical circuit structure,

these charging circuits having associated output conductors 0 through O respectively. All of the output conductors are connected to a common output terminal 20 which is connected to an input conductor 21 of a pulse generator 11.

Referring next to the detailed structure of pulse generator 11, the embodiment shown in Fig. 1 is essentially a regenerative amplifier including a normally non-conductive triode 22, having its plate circuit regeneratively coupled through a transformer 24 to its grid circuit. Under these conditions, whenever the grid of triode 22 becomes sufiiciently positive the triode is rapidly driven to a highly conductive state, because of positive feedback through the regenerative coupling, thereby causing production of a short electrical pulse (the pulse I at output conductor 12 of the amplifier output circuit. Asv shown in Fig. 1, input conductor 21 is connected to one end of a secondary winding 25 of transformer 24, the other end of this winding being connected to the grid of triode 22. A resistor 27 is connected between the grid and one terminal of a source (not shown) of potential V the other terminal of the source being grounded. The relationship between the potentials is V V V--that is voltage V is intermediate in magnitude between. voltage V and voltage V.

Understanding is best gained of the operation of pulse generator 11 in association with its plural charging circuits 1 through n by considering for a time the mode of operation obtained when an input signal is applied to only one of the charging circuits, charging circuit 1 being selected for purposes of example. For the purposes of the following explanation of operation it will be assumed that voltage V equals +100 volts, that voltage V equals +15 volts and that voltage V equals +25 volts.

' It will be assumed moreover that conductor 1 (and in fact all of the input conductors) are normally held at the low voltage level V of +15 volts, this voltage level rising abruptly to a value of +28 volts when an input signal (designated signal A is applied thereto. An illustrative voltage waveform of such a signal A is shown in Fig. 2. There are also shown in Fig. 2 on a common time scale corresponding voltage waveforms for the signal (designated signal Q) whichappears at terminal 1'5 of charging circuit 1 when signal A is applied, and for the resultant pulse signal I which appears upon output conductor '12.

It is clear that in the operation of charging circuit 1 the voltage level of signal Q corresponds to the voltage level to which capacitor C is charged by current flowing into it from the source of voltage V through resistor R In the normal condition of the charging circuit, before application of signal A to conductor 1 (conductor 1 therefore being at its lower level of +15 volts) capacitor C cannot charge to a voltage level above +1.5 volts for at that level diode D becomes strongly conductive and directly couples terminal '15 to conductor 1 thereby maintaining signal Q at +15 volts.

However, when signal A is applied, the voltage on conductor 1 rises abruptly to +28 volts, rendering diode D non-conductive. As a result, capacitor C is free to charge exponentially towards voltage V at a rate determined by the RC time constant of charging circuit 1. Theoretically capacitor C would charge to +28 volts before diode D would again become conductive and prevent further voltage rise. However, it will be shown that as soon as the voltage at terminal 15 (signal Q, as shown in Fig. 2) rises to the value of voltage V (+25 volts), pulse generator 11 will be fired producing an output signal I which marks the end of time interval x. Moreover at the same time that pulse I is produced pulse generator 11 kicks-back at charging circuit 1 (and in fact all of the charging circuits), by applying a large negative signal to its input conductor 21, this having the effect it will be shown of discharging all of'the charging circuit capacitors to voltageV It is important to understand why this kick-back pulse is produced and also to understand why pulse generator 11 fires as soon as signal Q rises to +25 volts. It might be thought that the voltage at which pulse generator 11 fires would be fairly indeterminate and very dependent upon the characteristics of triode 22. This is not the case. In actual operation very sharp exact firing of pulse generator 11 is obtained as soon as signal Q rises to voltage V (+25 volts), the exact point of firing being determined by the turn-over (transition from a non-conductive to a conductive state) of diode Ordinarily the grid of triode 22* is enough positive with respect to the cathode, that pulse generator 11 would reodes D in charging circuits 1 through 11 are non-conductive, thereby opening up any possible circuits for current flow through winding 25. However, referring again for purposes of example to charging circuit 1, when after application of signal A signal Q rises to +25 volts, diode D then turns over or becomes conductive. since its anode is then as positive as its cathode), thereby providing a circuit for current flow through winding 25. Pulse generator 11 then immediately regenerates strongly to apply output pulse I to output conductor 12. Moreover, it is clear that pulse generator 11' would also be fired in the same manner if a circuit for winding 25 were established by reason of any of the other diodes D (in charging circuits 2 through n) becoming conductive. Thus application of an input signal, such as signal A to any selected one of the charging circuits will cause pulse generator 11 to regenerate and fire for as soon as the voltage across the associated capacitor rises to +25 volts the corresponding diode D will be rendered C0117 ductive, thereby closing a circuit for winding 25 and thus initiating regeneration.

It will be recognized by those skilled in the art that during regeneration, a large voltage signal will be induced across secondary winding '25, the polarity of this voltage signal being such that a large positive signal is applied to the grid of triode 22 while at the same time a large negative signal (the kick-back signal) is applied back along input conductor 21 and through all of the diodes D to thereby discharge all of the charging circuit capacitors. Diodes D limit or clamp the negative excursion of the kick-back signal, these diodes becoming conductive as soon as the negative kick-back signal drops to voltage V and thereby clamping the signal at the voltagelevel V Thus in operation the net effect of the application of the kick-back signal to conductor 21 is to, simultaneously discharge all of the charging circuit capacitors C to their normal or starting level of. V volts.

As shown in Fig. 2, at the same time that the output pulse I is produced, signal Q (the voltage across capacitor C in charging circuit 1) is dropped abruptly to V volts (where V =+l5 volts) because of discharge of capacitor C by the accompanying kick-back pulse. It will be understood that each of the other charging circuit capacitors will be simultaneously discharged. in the same manner.

In the description of operation provided hereinabove, operation of time interval generating circuit 10 has been explained for that case in which input signal A is applied selectively to one of the charging circuits. It has been demonstrated thatupon application of the input signal, the associated charging circuit capacitor charges over a time interval x from an initial voltage, V to, a

voltage V at which pulse geenrator 11 fires producing,

the output pulse I and at the same time kicking back a large negative signal which has the eifect of discharging the capacitor (and' indeed all of the, charging circuit capacitors) to the initial voltage V Consider now what will occur when input signals are applied simultaneously to all of the chargi'ngcircuits along conductors 1 through n respectively. Upon application of these simultaneous input signals, each of the charging circuit capacitors will begin to charge upward from voltage V The rate of voltage rise will be greatest'in that charging circuit which has the shortest RC time constant. When a voltage level of V (+25 volts) is attained across the capacitor ofthis charging circuit, pulse generator 11 will fire and simultaneously discharge all of the capacitors to voltage V Thus, in operation, upon simultaneous application of input signals to all of the charging circuits,

the multiple charging circuits 1 through n is controlled by a single respectively associated analog input signal. However, it will be understood that the time constant of a charging circuit may be controlled by a plurality of analog input signals, the resultant time constant of the charging circuit representing the result of a mathematical function of the analog signals.

For example there is shown in Fig. 3, an embodiment of time interval generating circuit which includes a charging circuit 1a whose RC time constant is proportional to the sum of two analog input signals S and S As shown in Fig. 3, within charging circuit 1a, resistor R is provided as two serially connected variable resistors controlled in impedance magnitude by signals S, and S respectively. The total charging resistor R in charging circuit 1a is then proportional to the sum of analog signals S and S the time constant of the charging circuit therefore also being proportional to this sum. Another charging circuit 1b is also provided having its time constant controlled by analog signal S which varies a variable resistor and by analog signal S which varies an associated variable capacitor, so that the time constant of charging circuit 1b is proportional to the product of these analog signals. In the operation of the embodiment of time interval generating circuit 10 shown in Fig. 3, the time interval x produced by the circuit may correspond to the time constant of that charging circuit to which an input signal is applied. Alternately, if signals are applied simultaneously to both charging circuits, 1a and 1b, then the time interval x will be controlled by the charging circuit having the shortest time constant.

It is a matter of considerable importance that time intervals produced by a generating circuit of the present invention be accurately related to the time constant of the conrolling charging circuit. It is desirable to have this relationship reasonably independent of the precise values of the voltages supplied to the generating circuits. It will be demonstrated that such voltage independence can be obtained if voltages V, V and V are supplied in a fixed ratio to one another.

An arrangement of the described character is shown in Fig. 4 in which voltages V V and V, having a fixed ratio to one another, are shown as being supplied by a source 30 to a time interval generating circuit 10 of the type hereinbefore described whose resistor and capacitor are varied by corresponding analog signal (designated S and S As shown in Fig. 4, source 30 comprises a tapped resistor 32, which acts as a voltage divider. One terminal of resistor 32 is connected to ground while voltage V is applied to the other terminal of resistor 32. Voltage V is picked oif at this last named terminal and supplied to circuit 10. Voltages V and V are picked ofi at tape points 34 and 35 respectivel of resistor 32 and also supplied to circuit 10. It is seen that with the described circuit structure, voltages V V and V are in a fixed ratio to one another. Stating this algebraically it may be said that:

where k and k are fixed constants of proportionality.

Defining in Fig. 4 the voltage across capacitor C as the signal Q and remembering that the time interval x produced by circuit 10 corresponds to the time required for capacitor C to be charged from voltage V to voltage V there will now be derived an equation for the time interval x in terms of V, V V R and C. An illustrative voltage waveform of signal Q is shown in Fig. 5.

A differential equation describing the charging of capacitor C through resistor R is the following Equation 3:

v= 1214a idt 3 8 where i is the current flowing through resistor R. The solution to this differential equation has the following form:

Substituting from Equation 5 into Equation 4 there is obtained:

We are interested in finding the value of t at which the voltage Q across capacitor C has risen to the value V At this time, defined as the time x, the current i through resistor R must be equal to and therefore, substituting in Equation 6 there is obtained the following equation:

Solving Equation 7 for the time interval x, it is found that:

v- V, V- V It is clear from Equation 8, that if voltages V, V and V were supplied from independent sources, any variations in the absolute values of any of these voltages would affect the duration of the time interval x. However, according to the present invention voltages V, V and V are not independently supplied but are in a fixed ratio to one another as defined by Equations 1 and 2:

Substituting from equations (1) and (2) into Equation 8 there is obtained the equation:

:0: RC log,

V- 10 V :c-log m which may be rewritten in the form:

1 k .'1;--log (10) Thus, as indicated by Equation 10, the duration of time interval x is then independent of the precise value of voltages V, V and V Voltage V for example may be varied over wide ranges without affecting the duration of time interval x, since voltages V and V will continue to bear the fixed proportionality to voltage V described by Equations 1 and 2.

Referring again to Fig. 4, it should be noted in connection with time interval generating circuit 10 that if an input signal (such as signal A is continuously applied to input conductor cr. for a considerable time, circuit 10 will act during this time as a free running pulse producing circuit, producing pulses at a constant repetition rate, the time interval between successive pulses corresponding to the time interval x and therefore being proportional to the product RC. Moreover, because as described hereinbefore, voltages V, V and V are supplied in a fixed ratio to one another, this time interval and hence the pulse repetition rate will be independent of the absolute magnitudes of the supply voltages. In this manner a frequency or pulse repetition rate is produced which is proportional to L RC and substantially independent of the absolute values of supply voltages V, V and V Still other alterations, substitutions and additions to the present invention may be practiced by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed as new is:

1. A time interval generating circuit comprising: a plurality of passive element control circuits, each including an associated variable impedance element, each of said passive element control circuits being responsive to the application of an input signal for producing a control signal rising to a predetermined voltage after an associated time delay proportional in duration. to the magnitude of the associated variable impedance element; and a voltagesensitive signal generator responsive to said control signals for immediately producing a resultant output signal whenever any of said control signals attains said predetermined voltage, each of said control circuits including apparatus responsive to application of a predetermined kick-back signal for lowering the associated control signal to a predetermined reference voltage, said signalgenerator including first means for producing the predetermined kick-back signal whenever an output signal is produced and second means for applying the kick-back signal simultaneously to all of said control circuits whereby application of an input signal to any selected one. of said passive element control circuits causes saidtsignal generator to produce an output signal after the time delay associated with the selected control, circuit while simultaneous application of input signals to all of said control circuits causes said signal generator to produce an output signal after a time interval corresponding to the shortest of the associated time delays.

2. A time interval generating circuit comprising: a signal generator having first and second terminals and operable for producing an output signal whenever a conductive circuit is wtablished between said first and second terminals; a plurality of passive element control circuits each including a variable impedance element and having a normal starting state, each of said control circuits being coupled to said first and second terminals and being operable in response to application of an input signal for forming a conductive circuit between said first and second terminals after an associated time delay proportional to the magnitude of the corresponding impedance element, said control circuits being responsive to each output signal for returning all control circuits to the normal starting state whereby application of an input signal to any selected one of said passive element control circuits causes said signal generator to produce an output signal after an interval equal to the time delay associated with the selected control circuit and simultaneous application of input signals to all of said control circuits causes said signal gen- 10 erator to produce a single output signal after an interval equal to the shortest of the associated time delays.

3. A time interval generating circuit comprising: a signal generator having first and second terminals and operable for producing an output signal whenever a conductive circuit is established between said first and second terminals; a plurality of passive element control circuits each including a variable impedance element, each of said control circuits being coupled to said first and second tenninals and being operable in response to application of an input signal for forming a conductive circuit between said first and second terminals after an associated time delay proportional to the magnitude of the corresponding impedance element, each of said control circuits including a capacitor normally charged to a voltage level V and also including means responsive to application of the input signal for charging said capacitor towards a predetermined voltage level V at a rate inversely proportional to the magnitude of the corresponding impedance element, said time interval generating circuit further including voltage responsive apparatus connected to said capacitor and intercoupling said first and second terminals, said voltage responsive apparatus being operable for forming a conductive circuit between said terminal whenever said capacitor is charged to a predetermined voltage level V whereby application of an input signal to any selected one of said passive element control circuits causes said signal generator to produce an output signal after an interval equal to the time delay associated with the selected control circuit and simultaneous application of input signals to all of said control circuits causes said signal generator to produce an output signal after an interval equal to the shortest of the associated time delays.

4. The time interval generating apparatus defined by claim 3 wherein said signal generator includes means for applying a discharge signal to all of said control circuits, at each production of an output signal, to discharge all of said capacitors to the voltage level V 5. The time interval generating apparatus defined by claim 3 wherein said voltage responsive apparatus includes a normally non-conductive rectifier element coupled to said capacitor and further includes means for rendering said rectifier element conductive whenever said capacitor is charged to the predetermined voltage level V 6. A time interval generating circuit comprising: a source of potentials V V and V, where V is intermediate in magnitude with respect to V and V; a plurality of charging circuits, each including a capacitor for producing a potential Q proportional to the integral of current applied thereto, impedance means responsive to potential Q and potential V for applying current to said capacitor proportional to the quantity V-Q, and a discharge circuit receiving said potential V and responsive to the application of a predetermined discharge signal for rapidly discharging said capacitor until potential Q becomes equal to potential V a signal generator actuable for producing an output signal and for simultaneously applying the predetermined discharge signal to all of said discharge circuits; and an actuating circuit responsive to potential V and each of the potentials Q for actuating said signal generator whenever a potential Q becomes equal to potential 7. A time interval generating circuit for producing a series of output signals at time intervals proportional to the magnitude of an impedance element and independent of the absolute magnitude of operating potentials supplied thereto, said interval generating circuit comprising: a source of operating potentials for producing potentials V V and V having fixed ratios relative to one another, potential V being intermediate in magnitude with respect to potentials V and V; a capacitor impedance element responsive to the application of current thereto for producing an output potential Q proportional to the integral of the applied current and inversely proportional to the magnitude of said capacitor element; a resistor impedance element responsive to potentials V and Q for applying to said capacitor element current proportional to the quantity V-Q and inversely proportional to the magnitude of the resistor impedance element; a signal generator operable. in response to potentials Q and V for producing an output signal whenever potential Q equals potential V discharge means receiving potential V and responsive to each operation of said signal generator for simultaneously discharging current from said capacitor impedance element until potential Q equals potential V whereby a series of output signals are produced by said signal generator occurring at time intervals proportional to the magnitudes of said impedance elements and independent of the absolute magnitudes of potentials V V and V.

8. The time interval generating circuit defined by claim 7 wherein said source of operating potentials includes apparatus for producing potentials V V and V having a fixed relationship to one another such that the quantity VV is proportional to the quantity VV 9. The time interval generating circuit defined by claim 7 wherein said resistor impedance element is variable in magnitude, said generating circuit further including means for varying said impedance element in accordance with a predetermined function of an applied analog signal, whereby time intervals between successive output signals are proportional to the predetermined function of the analog signal.

10. The time interval generating circuit defined by claim 7 wherein said capacitor impedance element is variable in magnitude, said generating circuit further including means for varying said capacitor element in accordance with a predetermined function of an applied analog signal, whereby the time intervals between successive output signals are proportional to the predetermined function of the analog signal.

11. A time interval generating circuit comprising: a signal generator having first and second terminals and operable for producing an output signal whenever a conductive circuit is established between said first and second terminals; a plurality of passive element control circuits each including a variable impedance element, each of said control circuits being coupled to said first and second terminals and being operable in response to application of an input signal for forming a conductive circuit between said first and second terminals after an associated time delay proportional to the magnitude of the corresponding impedance element, said signal generator comprising a regenerative amplifier including a feedback winding interconnected between said first and second terminals, whereby application of an input signal to any selected one of said passive element control circuits causes said signal generator to produce an output signal after an interval equal to the time delay associated with the selected control circuit and simultaneous application of input signals to all of said control circuits causes said signal generator to produce an output signal after an interval equal to the shortest of the associated time delays.

12. A time interval generating circuit comprising: a plurality of independent passive control circuits, each including an associated variable impedance element, and means for applying a potential to said variable impedance element, a corresponding plurality of input signal conductors, each being connected to a different one of said control circuits, each of said passive element control cir cuits being responsive to the application of a different input signal on the corresponding conductor connected thereto for producing a control signal rising to a predetermined voltage after an associated time delay proportional in duration to the magnitude of the associated variable impedance element; and a voltage sensitive signal generator commonly responsive to said control signals for immediately producing a resultant output signal Whenever any of said control signals attains said predetermined voltage whereby application of an input signal to any selected one of said passive element control circuits causes said signal generator to produce an output signal after the time delay associated with the selected control circuit while simultaneous application of input signals to all of said control circuits causes said signal generator to produce an output signal after a time interval corresponding to the shortest of the associated time delays.

13. The time interval generating circuit defined by claim 12 wherein each of said control circuits includes means responsive to applied analog input signals for varying its associated impedance element in accordance with a predetermined mathematical function of applied analog input signals.

14. The time interval generating circuit defined by claim 13 wherein at least one of said variable impedance elements comprises a resistor.

15. The time interval generating circuit defined by claim 13 wherein at least one of said variable impedance elements comprises a capacitor.

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